Excess body weight is a major public health crisis in the United States and worldwide. Although the essential cause for obesity is an imbalance in energy intake v. expenditure, the indirect causes leading to this imbalance are complex and multifaceted. Numerous studies have found that insufficient sleep increases risk of weight gain and unhealthy behavioral patterns (increased caloric intake, decreased physical activity). Stress is also an important indirect factor for obesity, and stress and sleep deficiency exacerbate one another. Unfortunately, very little is known about how stress and sleep interact and manifest behaviorally for individuals in the natural environment. Findings from this study will contribute t the scientific literature base by providing data about the interrelationships between social rhythms, sleep and weight gain after involuntary job loss, a life event that is often stressful and disrupting to an individual's daily routine. The investigative team will enroll 250 participants ina prospective, longitudinal 18-month design. They will employ gold-standard assessments of social rhythms, sleep, weight gain, and dietary intake and energy expenditure in order to further specify the mechanisms by which weight gain occurs. They will also employ multivariate, growth curve modeling to elicit valuable information about the temporal precedence of changes in social rhythms, sleep, and weight gain. It is proposed that: (1) unemployed individuals with less consistent social rhythms and worse sleep will have steeper weight gain trajectories over 18 months than unemployed individuals with stable social rhythms and better sleep; (2) disrupted sleep mediates the relationship between social rhythm disruption and weight gain; and (3) reemployment is associated with a reversal in the negative trajectories outlined above. Overall support for these aims will indicate that sleep and social rhythms operate as mechanisms of weight gain in the aftermath of involuntary job loss. Moreover, these findings will advance obesity research by testing the interrelationships among daily behavioral activity, sleep, and stress in the natural environment. Positive findings will provide solid support for the development of prevention campaigns targeting sleep and social rhythms in an accessible subgroup of vulnerable individuals.